1. Field of Application
The application relates to a silicone epoxy, and more particularly to a transparent silicone epoxy composition applied on a light emitting diode package.
2. Description of Related Art
The light emitting diode (LED) has the advantages of power saving, small volume, long life-time (hundred-thousand hours), fast response, low pollution, high reliability and large module flexibility so that LEDs are widely applied in the technical fields. Currently, with the progressive technology development, the efficiency and the brightness of the LEDs are continuously enhanced so that the application range is enlarged to cover the backlight module of the display and the light source of the vehicles. In the near further, it is possible for the LEDs to replace the fluorescent lamp to be the next-generation light source. Further, the LEDs with the high power and high brightness become the main stream of the future development and the demands on them gradually increase.
However, under the high operation temperature of the high power operation of the LEDs, the efficiency of the LEDs decreases due to the thermal-yellowing phenomenon of the transparent molding compound of the LEDs. Moreover, both of UV LED and blue-ray LED generate high-energy radiations with short wavelengths and these radiations with short wavelengths leads to the photo-yellowing phenomenon of the transparent molding compound of the LEDs. Furthermore, as for the LEDs applied on the outdoor devices, such as the streetlamps or the headlights of the vehicles, not only the sunlight leads to the yellowing phenomenon of the transparent molding compound of the LEDs, but also the gas, such as oxygen, in the open environment damages the molding compound and the internal elements enclosed by the molding compound. Thus, the life-time of the elements is affected.
Conventionally, the transparent molding compound for the LED packages are the composition of epoxy resin and anhydride. The epoxy resin-anhydride composition has the advantages of good mechanical property, good adherence and low cost. However, anhydride is sensitive to the moisture and is easily converted to the organic acid while being moisturized. Thus, the reactivity of anhydride varies, which leads to degration of the physical nature of the composition. Meanwhile, the chemical bonding energy of epoxy resin to anhydride is relatively low so that the yellowing phenomenon easily happens under high temperature operation for a long time, which leads to decreasing of the transparency of the molding compound. That is, the yellowing phenomenon of the epoxy resin-anhydride composition easily happens due to the high temperature or the UV radiation which limit the applications of the epoxy resin-anhydride composition on the high power LED packages. Moreover, the silicone resins has the advantages of good photo durability and good heat durability, so that the silicone resins are mainly applied on the high power LED packages. However, the silicone resins has the disadvantages of poor mechanical property, tacky surface which easily leads to the adsorption of particles in the atmosphere. Therefore, the transparency and the light-extraction efficiency of the silicone resin decrease. Further, poor adherence and poor air-barrier ability of the molding compound easily lead to erosion of the metal wires of the elements. Also, under the conditions of high temperature and high humidity, the molding compound is easily atomized which leads to the risk of the reliability in long-time usage.